Adrian Peterson's future with the Minnesota Vikings dimmed further Tuesday, with the NFL suspending the star running back without pay for at least the rest of the season.

As his representatives initiated an appeal, Peterson remained at the center of an escalating dispute between the league and the NFL Players Association over the player discipline process.

Commissioner Roger Goodell told Peterson he will not be considered for reinstatement before April 15 for his violation of the NFL personal conduct policy -- the first example of a crackdown on players involved with domestic violence.

The NFLPA quickly announced it would immediately appeal, calling for a neutral arbitrator to handle it, and sharply rebuked the league for what it labeled as inconsistency and unfairness in determining the discipline. The NFL's words were even stronger, with a nearly 1,600-word statement spelling out the conditions for Peterson's path to return to the field and describing the reasons for the stiff punishment.

Peterson pleaded no contest Nov. 4 to misdemeanor reckless assault in Texas for injuries to his 4-year-old son with a wooden switch. He said he intended no harm, only discipline. Peterson was on a special exempt list at the sole discretion of Goodell, essentially paid leave while the case went through the legal system.

The NFLPA said Peterson was told that would count as time served toward a suspension, citing an unidentified NFL executive. League spokesman Brian McCarthy said the stay on the exempt list was taken into account.

"There were aggravating circumstances that led to the discipline announced," McCarthy said.

Peterson's salary for the season was $11.75 million. He will keep the money accrued while on the exempt list. But the NFL's punishment has now amounted to a 14-game ban, with six unpaid weeks. That's the equivalent of a fine of more than $4.1 million.

Peterson's agent, Ben Dogra, told The Associated Press he and his client were scheduled for a conference call Tuesday with the NFLPA to discuss options.

"We look forward to filing an immediate appeal and coming to a resolution for Adrian Peterson that would be appropriate under the circumstances," Dogra said.

The Vikings don't practice Tuesdays. The organization issued a brief statement: "We respect the league's decision and will have no further comment at this time."

Goodell announced Aug. 28 tougher punishment for players involved with domestic violence. That action stemmed from a torrent of criticism for the initial leniency toward Baltimore Ravens running back Ray Rice following a caught-on-camera knockout punch of the woman who is now his wife. Rice was later suspended indefinitely and recently had his appeal heard by an arbitrator.

According to the enhanced policy, first offenses of assault, battery or domestic violence bring a six-game suspension. Aggravating circumstances warrant higher levels of discipline, and Goodell's letter to Peterson spelled that out.

Goodell pointed to the child's age and the significant physical difference between Peterson and his son.

"Further, the injury inflicted on your son includes the emotional and psychological trauma to a young child who suffers criminal physical abuse at the hands of his father," Goodell wrote. "Second, the repetitive use of a switch in this instance is the functional equivalent of a weapon, particularly in the hands of someone with the strength of an accomplished professional athlete."

Goodell also came down on Peterson for showing "no meaningful remorse" for hurting the boy and expressed concern that he "may feel free to engage in similar conduct in the future."

The injuries to the boy occurred in May. Peterson was indicted on a felony child abuse charge in September, a few days after rushing for 75 yards in the season opener. The Vikings put him on the inactive list for the next game, just as they would for players who are injured or backups. The day after, they announced he would resume playing until completion of his due process in court.

But with the Rice backlash as a backdrop, Peterson, the Vikings and the NFL were inundated by protest, including corporations canceling sponsorships. The Vikings relented and less than two days later the league placed him on the exempt list.

The union has accused the league of overstepping bounds spelled out in the collective bargaining agreement.

"The decision by the NFL to suspend Adrian Peterson is another example of the credibility gap that exists between the agreements they make and the actions they take. Since Adrian's legal matter was adjudicated, the NFL has ignored their obligations and attempted to impose a new and arbitrary disciplinary proceeding," the NFLPA said.

Peterson will turn 30 in March. There are three years and $45 million remaining on his contract, but none of it is guaranteed. The Vikings would take only a $2.4 million hit on their 2015 salary cap if they cut him before next season.

The NFL said Peterson would stay on the exempt list and continued to be paid during the appeal process.

The two sides took part in a conference call Monday regarding a grievance the union filed against the league for keeping Peterson on the exempt list after the plea agreement was reached. The arbitrator on that issue will rule this week. But the NFL's suspension Tuesday has minimized the significance of the grievance.

Even if Peterson were to be reinstated to the roster during the appeal process, the Vikings actually playing him would be an unlikely scenario given the heat they've taken and the long time Peterson has been away from the team. The Vikings (4-6) have six games left and host the rival Green Bay Packers Sunday.